1. Field of the Invention
The invention pertains to high frequency phase shifter elements and more particularly to digital diode phase shifter elements of the transmission line type wherein a capacitor is coupled serially in the primary transmission line conductor.
2. Description of the Prior Art
In modern high frequency radar and communication systems, the antenna pattern must be moved at very rapid rates and this is normally achieved in array antennas by use of a matrix of small radiators whose radiation phases are systematically and electronically varied. The necessary phase gradients across the antenna are usually generated in discrete steps by a plurality of such electronic phase shifter elements.
A major handicap in the past phase shifter elements has been in the inability exactly to reproduce the diodes upon which the characteristics of the diode phase shifter elements are significantly dependent. However, this problem has been essentially solved by semiconductor manufacturers, so that attention turns to the improvement of the phase shifter elements themselves. The design of the present phase shifter element permits it beneficially to be physically smaller than conventional elements of the loaded transmission line type, for example. The invention avoids the use of complex implementation, none of the prior art very high impedances and no very low impedance lines being required, so that a satisfactory, non-critical high frequency structure on one side of the element is readily achieved. No fine conductor lines are required as in reflective phase shifters using directional couplers. As well as calling for simpler high frequency circuits, the low frequency and bias control arrangements are all disposed on the second or grounded side of the element. The novel phase shifter element is also found to possess fully adequate band width for use in electronically steerable, phased array antennas and in kindred applications.